Esm223 20 Reference - Diamondoids - nanodiamonds - LLNL Feb2008

DIAMOND, a form of crystalline carbon, has long been treasured as a precious jewel. However, for many years, tiny diamond particles, equivalent to a billionth of a billionth of a carat, have plagued oil workers when the particles clump together and clog pipelines. These particles, called diamondoids, can be found in crude oil at concentrations up to thousands of parts per million. Similar diamondlike carbon nanoparticles occur in meteorites, interstellar dust, and protoplanetary nebulae. High-explosive detonations have produced much larger, less pure diamond nanoparticles. A team of Livermore researchers led by physicist Trevor Willey is helping to transform diamondoids from pesky pipeline sludge and astronomical curiosity into building blocks for new materials. The researchers are also investigating the microscopic particles’ fundamental electrical properties, which could lead to their use in electronic devices. Diamondoids comprise one to many units of the compound adamantane (from “adamas,” the Greek word for diamond). First discovered in 1933, adamantane is the smallest cage structure of the diamond crystalline lattice, consisting of 10 carbon atoms and 16 hydrogen atoms. A single adamantane molecule terminates in atoms of hydrogen. However, when the units repeat billions of times in three dimensions, the carbon atoms of other adamantane cages replace the terminal hydrogen atoms, forming the bulk diamonds used in jewelry and industry. Adamantane, diamantane (two units of adamantane), and triamantane (three units) are referred to as lower diamondoids because each has only one shape. The “higher” diamondoids—those with more than three linked adamantane units—can assume several possible shapes. The lower diamondoids can be easily synthesized, but chemical synthesis of larger diamondoids has proven impossible except for one form of tetramantane (four units of adamantane).

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Diamondoids as Semiconductors Livermore’s diamondoid work is an outgrowth of semiconductor research that began in the mid-1990s with funding from the Laboratory Directed Research and Development Program. A semiconductor is a crystalline solid exhibiting electrical properties between those of metals and insulators. In that initial project, Willey worked with physicist Tony van Buuren and postdoctoral researcher Christoph Bostedt (now at the Technical University of Berlin) to determine how quantum confinement affects the electronic properties of silicon and germanium.

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